On 16/08/2022 14:01, Simon Josefsson wrote:
Hi.
I noticed a (to me) unexpected difference between bash and dash, compare
bash behaviour:
jas@latte:~$ mkdir -p foo foo/bar
jas@latte:~$ cd foo/bar
jas@latte:~/foo/bar$ command -v ../bar
jas@latte:~/foo/bar$ echo $?
1
jas@latte:~/foo/bar$
with dash behaviour:
$ mkdir -p foo foo/bar
$ cd foo/bar
$ command -v ../bar
../bar
$ echo $?
0
$
That is, dash's 'command -v' return success on directories for relative
names.
It's not relative vs absolute, it's because names that don't involve /
involve PATH lookup. If you try 'command -v /', dash will also print /.
I believe the dash behaviour is incorrect, but I'd appreciate if
someone else read the POSIX spec here. Do you agree?
Sadly, I don't. I think the current behaviour is what POSIX technically
requires, and at the same time that what POSIX requires is bad and shell
authors should use common sense and not implement it as written.
POSIX says for command -v:
> Utilities, regular built-in utilities, command_names including a
<slash> character, and any implementation-defined functions that are
found using the PATH variable (as described in Command Search and
Execution), shall be written as absolute pathnames.
../bar is a command_name including a <slash> character. There is nothing
in here that says to check whether it is executable, POSIX just says to
write it as an absolute pathname, and that is what dash does.
Even if this text is read as deferring to Command Search and Execution,
that says:
> If the command name contains at least one <slash>, the shell shall
execute the utility in a separate utility environment with actions
equivalent to calling the execl() function [...]
There is no "check if it is an executable file" here either, the shell
is supposed to just execl() the directory and report the error. And in a
way, it kind of makes sense that command -v reports that that is what
the shell would attempt.
Despite this, dash is pretty much the only shell that behaves this way
and I would encourage changing it to match other shells.
This is on Debian bullseye with dash 0.5.11+git20200708+dd9ef66-5 and
bash 5.1-2+deb11u1.
/Simon
Cheers,
Harald van Dijk
